The present disclosure generally relates to gas purification systems and processes of use, wherein an acid component entrained in a flue gas, for example, is separated by wet chemical absorption. In particular, the present disclosure relates to systems and processes configured to utilize low pressure steam as a heat source.
In conventional industrial technologies for gas purification, impurities, such as H2S, CO2 and/or COS are removed from a gas stream such as flue gas, natural gas, syngas or other gas streams by absorption in a liquid solution, e.g., in a liquid solution comprising ammonia and/or one or more amine compounds.
Used liquid solution is subsequently regenerated in a regenerator column to release the impurities comprised in the solution, typically by countercurrent contacting with steam. The steam needed for regeneration is typically produced by power plant turbine system. In addition, a reboiler in fluid communication with the regeneration column may provide further release of impurities comprised in the liquid solution.
In conventional absorption-regeneration processes as described above, regenerated and reboiled liquid solution are typically re-used in another absorption cycle. The reboiled solution may however have a temperature as high as 100-150° C. To enable efficient absorption, the liquid absorbent solutions typically requires cooling before being passed to another round of absorption. Cooling has conventionally been accomplished by heat-exchange with the used liquid solution from absorption.
In general, the energy requirements of a conventional gas purification process are of three types: binding energy, stripping energy and sensible heat. Binding energy is required for breaking the chemical bond formed between the impurities and the liquid solution, whereas stripping energy is required for releasing the impurities from the liquid solution. Sensible heat is in turn needed for heating of the liquid solution prior to regeneration.
In the conventional absorption-regeneration systems and processes, it has been shown that ammonia efficiently removes CO2, as well as other contaminants from a flue gas stream. In one particular application, absorption and removal of CO2 from a flue gas stream with ammonia is conducted at low temperature, for example, between 0 and 20° C. In these types of systems, which are often referred to as a chilled ammonia based systems, the demand on heat required for solvent regeneration is usually covered by steam that condenses on the steam side of the reboiler. The steam is usually taken from the water/steam cycle of the power station. However, steam is mostly extracted from the intermediate pressure/low pressure crossover pipeline between the outlet of the intermediate pressure (IP) turbine and the inlet of the low pressure (LP) turbine. One reason is that the pressure level present in the IP/LP crossover pipeline is applicable for solvent regeneration. However, extracting IP steam from these locations within the power plant causes a penalty in the generation of electricity.